Disconnected street networks were the default, entrenched pattern of development in post-WWII America. However, by the early 1960s a backlash had arisen in opposition to the conventional planning wisdom. This countermovement snowballed through the 60s and 70s, and by the 1980s the issue had filtered into the architectural profession and scholarly research.

Part II of this series described how disconnected street patterns became ubiquitous in U.S., with the mandate in particular coming from the Federal Housing Administration. By 1941, over 200 cities had instituted subdivision regulations that encouraged disconnected street patterns.

The building industry helped to codify and entrench those standards nationwide. The Urban Land Institute (ULI) published recommendations in 1947 that promoted disconnected patterns. The Institute for Transportation Engineers’ (ITE) Recommended Practice for Subdivision Streets (1965) recommended discontinuous local streets. In ITE publications through the 1980s and 1990s, recommendations for low connectivity remained unchanged. ITE standards were adopted wholesale by public works departments throughout the nation. More than any other single source, ITE publications directed the street patterns of U.S. development in the late twentieth century.

Meanwhile, the visionary wing of the architectural profession was launched on a trajectory of the fantastic, drawing deeply from pulp science fiction and heroic feats of gigantic engineering. Ideas for the metropolis of the future encompassed cities floating on the ocean and resting on the ocean bottom, cities drifting in the air, mobile cities, and modular cities whose component parts could split off, travel to other parts of the world, and recombine with other modules to form new, instant cities. The thread running through many of these proposals was that of a lifestyle entirely divorced from the ground, from the rhythms of the natural world, and from human scale and walking. All life was to be machine-mediated and pedestrian networks were superfluous.

It wasn’t until the car culture had assumed complete hegemony in America that Jane Jacobs revisited street connectivity and its relationship to successful, vital cities.

Jacobs was a writer who eventually became one of the leading thinkers and activists for city life and pedestrian-oriented streets. In The Death and Life of Great American Cities (1961), Jacobs wrote that the greatness of cities is based on their diversity — diversity in enterprises, retail trade, cultural facilities, and entertainment. She championed the small and the idiosyncratic: small manufacturers, small offices, specialized shops, art movies, nightclubs, etc. She said that great variety in commerce is related to variety in cultural opportunities, streetscapes, and populations.

Four conditions are indispensable for generating city diversity:

Mixed use serving different functions and schedules

A mix of old and new buildings

High population density

Short blocks — Jacobs’ exact quote is “Most blocks must be short; that is, streets and opportunities to turn corners must be frequent.”

For Jacobs, small blocks were essential for a simple reason: Blocks that were too big made walking inconvenient. There was no reason to make a lengthy detour around a big block. Where blocks were too long, pedestrians were channeled into the same routes every day. That made walking dull, constrained street life, and limited the area where storefronts could be successful. Not only do vital areas require small blocks, but routes must be continuous as well. “In city districts that become successful and magnetic, streets are virtually never made to disappear,” wrote Jacobs.

In support of her argument, Jacobs presented examples from sections of Manhattan, Philadelphia and Washington, D.C. Frequent streets are a means to an end, she wrote:

The means by which they work (attracting mixtures of users along them) and the results they can help accomplish (the growth of diversity) are inextricably related. The relationship is reciprocal.

— The Death and Life of Great American Cities, p. 186

Christopher Alexander, in his influential essay A City is Not a Tree (1965), argued against dendritic (tree-like) patterns in urban planning. Alexander addressed tree-like patterns in several realms — social, political and physical. However, his examples and illustrations focused on street networks and land use mix. Alexander wrote that planning philosophies underlying tree-like patterns are authoritarian, artificial and inhumane. The dendritic organization of space fails to correspond to social realities and is psychologically damaging.

Many of the writers of the 50s and 60s who were advocating a more human-scale, pedestrian-oriented urban design had support from the Rockefeller Foundation. These included Jane Jacobs, Christopher Alexander, Christopher Tunnard, Ian Nairn, Edmund Bacon and others.

Throughout the following decades the backlash against disconnected street networks gathered steam as part of a greater movement to reclaim the importance of walkability in urban design. Léon Krier’s theoretical designs and advocacy in the U.S., and Jan Gehl’s pedestrian research published in Life Between Buildings (1971) were influential.

A handful of urban plans were adopted and developments broke ground, based on networks of small blocks and connected streets. Some of these included the St. Lawrence Neighborhood Plan in downtown Toronto (1975), the Randolph Neighborhood in Richmond, VA (1977), Battery Park City in Manhattan (1979), and Seaside in the panhandle of Florida (1981).

By the 1990s, codes and standards for connectivity were starting to be adopted by municipalities and standards-setting organizations. Significantly, the Institute of Transportation Engineers published its first set of alternative standards as a “proposed recommended practice” intended to support walkability: Traditional Neighborhood Development Street Design Guidelines (1997). After 60 years of disconnected, dendritic street patterns, it looked as if a few in the professions might consider alternatives. But the force of inertia was strong; the shift to alternatives has been slow in some quarters, while the bias toward automobile orientation has continued unabated in others.

2 Responses to “Connectivity Part 3: Latter Half of the 20th Century”

Several years ago, I asked a math-whiz friend to develop a formula for determining the number of possible routes through a complex street network. I call his formula the “Hawthorne Traffic Equation”, and use it in presentations. It is a factoral equation: (x+y)!/x!y! = # of possible routes, where x is the number of east west blocks and y the number of north south blocks. Note, this formula does not allow for doubling back. If it did the number of possible routes is MUCH greater. Victor Dover put it in a handy graphic. Let me know if you’d like a power point copy.